1. Field of the Invention (Technical Field)
The present invention is an electrolytic method and apparatus for desolving carbonate scale and preventing biofilm formation on surfaces.
2. Background Art
Note that the following discussion refers to a number of publications and references. Discussion of such publications herein is given for more complete background of the scientific principles and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Calcium carbonate formation and biofilm growth on surfaces of process equipment, piping systems, and other applications is a leading cause of maintenance and operational failure of these systems. As an example, ultraviolet light (UV) systems have proven to be very effective for destruction of microorganisms, organics, chemicals, and other compounds in fluid treatment systems, notably, water treatment systems. In nutrient rich environments, UV provides an excellent energy source for growth of biofilms and algae on UV quartz tubes. Many systems today utilize expensive scraper mechanisms for wiping the quartz tubes to clean carbonate scale and biofilm from the quartz tube surfaces. U.S. Pat. No. 5,874,740 by Ishiyama describes such a scraper system for cleaning an ultraviolet tube.
Electrolytic technologies utilizing dimensionally stable anodes have been developed to produce mixed-oxidants and sodium hypochlorite solutions from a sodium chloride brine solution. Dimensionally stable anodes are described in U.S. Pat. No. 3,234,110 to Beer, entitled “Electrode and Method of Making Same,” wherein a noble metal coating is applied over a titanium substrate. In the 1990s, research by Dr. Greg Swain at Michigan State University has demonstrated that diamond coated electrodes offer significant improvements in durability over conventional dimensionally stable anodes. U.S. Pat. No. 4,761,208 by Gram, et al describes an electrolytic method and cell for sterilizing water. An electrolytic process can be used to produce these oxidants from aqueous solutions having a wide range of total dissolved solids in solution.
Furthermore, U.S. Pat. No. 5,308,507 by Robson describes a mixed-oxidant generation method and apparatus for removing organic contaminants utilizing a combination of mixed-oxidants and ultraviolet light. It is well known that the oxidant solution produced at the anode of the electrolytic cell has a low pH value, typically in the range of 2 to 3 pH. The cathode surface typically has a high pH value at the surface, usually in the range of 12 to 13 pH. It is also well known that calcium carbonate scale formation cannot occur at the anode due to the low pH conditions at the anode surface. However, calcium carbonate scale formation can occur at the cathode surface, particularly if calcium is present in the water as an ion flowing through the electrolytic cell. Some electrolytic cells, particularly those used for swimming pool applications, utilize this feature to de-scale the cathode by periodically reversing the polarity of the cell electrodes, effectively changing the cathode to the anode. A low pH acidic solution now formed at the surface of the anode (formerly the calcium carbonate-loaded cathode) dissolves the calcium carbonate.
This electrolytic oxidant feature of generating a low pH condition at the anode can be utilized to prevent scale buildup at the surface of UV tubes and other process equipment.